Like Keith said, the fan in the power supply isn't user serviceable, it's one big honkin' unit.
Regarding RMA, yes, the PEM should be RMAd. The fan tray is there to cool the main chassis section (line cards, REs), not the power supplies, so heat from the power supply itself isn't being dealt with properly with the PEM's fan broken. It may run for a while without the fan but its lifetime is unknown with hot spots building up inside it.
-Chad